The impact of triclosan on the spread of antibiotic resistance in the environment

Abstract

Triclosan (TCS) is a commonly used antimicrobial agent that enters wastewater treatment plants (WWTPs) and the environment. An estimated 1.1 × 10(5) to 4.2 × 10(5) kg of TCS are discharged from these WWTPs per year in the United States. The abundance of TCS along with its antimicrobial properties have given rise to concern regarding its impact on antibiotic resistance in the environment. The objective of this review is to assess the state of knowledge regarding the impact of TCS on multidrug resistance in environmental settings, including engineered environments such as anaerobic digesters. Pure culture studies are reviewed in this paper to gain insight into the substantially smaller body of research surrounding the impacts of TCS on environmental microbial communities. Pure culture studies, mainly on pathogenic strains of bacteria, demonstrate that TCS is often associated with multidrug resistance. Research is lacking to quantify the current impacts of TCS discharge to the environment, but it is known that resistance to TCS and multidrug resistance can increase in environmental microbial communities exposed to TCS. Research plans are proposed to quantitatively define the conditions under which TCS selects for multidrug resistance in the environment.

Keywords: antibiotic resistance; antimicrobial resistance; biosolids; triclosan; wastewater.

FIGURE 1

Triclosan exposure increases resistance to antibiotics. Minimum inhibitory concentrations of chloramphenicol and tetracycline for control strains (striped bars) and TCS adapted strains (solid bars) are shown from various studies and bacteria. Differences were observed in most cases, however, no difference was found for tetracycline resistance for Salmonella enterica in the study by Birosová and Mikulásová (2009). Chloramphenicol resistance was not tested in Pseudomonas aeruginosa (Chuanchuen et al., 2001).

FIGURE 2

The MIC of TCS-acclimated and TCS-unacclimated strains relative to environmental TCS concentrations. Open symbols represent the MIC for TCS sensitive strains, while closed symbols represent the MIC for TCS adapted strains. Black bars are ranges of TCS concentrations found in each environmental setting. Biosolids concentrations were converted from mg/kg to mg/L by assuming 3% total solids in reactors that produce biosolids (McMurry et al., 1998a, 1999; Chuanchuen et al., 2001; Slater-Radosti et al., 2001; Fan et al., 2002; Yazdankhah et al., 2006; Karatzas et al., 2007; Mima et al., 2007; Tkachenko et al., 2007; Bailey et al., 2008; Webber et al., 2008; Chalew and Halden, 2009; Chen et al., 2009; McClellan and Halden, 2010; Yu et al., 2010; Saleh et al., 2011; Bedoux et al., 2012).